Metal-oxygen batteries, which are also referred to as metal-air batteries, are a class of electrochemical cells in which oxygen, which is typically obtained from the ambient environment, is reduced at a catalytic cathode surface as part of the electrochemical cell reaction. Reduction of the oxygen forms an oxide or peroxide ion which reacts with a cationic metal species. Metal-oxygen batteries have been developed based upon Fe, Zn, Al, Mg, Ca, and Li. It is acknowledged that in the strictest sense a “battery” is an electrochemical device comprised of a number of separate electrochemical cells interconnected to a single set of terminals to provide an output which is cumulative in terms of voltage and/or current of each of the individual cells. However, for purposes of the present disclosure, and in keeping with vernacular terminology, the term “battery” will be used herein to define electrochemical power generation and/or storage devices comprised of single cells as well as plural, interconnected cells.
Lithium-oxygen batteries represent one type of metal-oxygen battery. In devices of this type, an electro-active cathode and a lithium-containing anode are disposed in an electrolyte which provides for ionic communication therebetween. During the discharge of the cell, oxygen is reduced at the electro-active cathode to produce O−2 and/or O2−2 ions which react with the lithium to produce Li2O2 and/or Li2O which deposits on the cathode. Such cells provide an operating voltage in the typical range of 2.0–2.8 V, and an open circuit voltage of 2.85 V, and they have a good charge storage capacity, typically on the order of 1500–2000 mAh/g. However, the reduction of O2 and the deposition of Li2O2 or Li2O is relatively slow. Hence, the discharge and charge rate of batteries of this type is relatively low, which limits their use in particular applications.
In another type of lithium battery, the cathode thereof is fabricated from a crystalline or semi-crystalline material which is capable of intercalating lithium into the lattice structure thereof during the discharge cycle. The intercalation reaction is a fast process that allows the cathode to discharge at a high rate, but the capacity of such electrode materials to intercalate lithium is typically limited to about 120–250 mAh/g. Hence, batteries of this type are relatively large as compared to comparable batteries employing cathodes which reduce oxygen.
The present invention provides a hybrid battery cathode which combines materials which intercalate lithium or other metals along with materials which can reduce oxygen so as to allow the battery to also operate in a metal-oxygen mode. Batteries of the present invention combine high charge and discharge rate capabilities together with good charge storage capacity. While various of the materials employed in the present invention have been utilized, individually, in cathodes of the prior art, the prior art has not been directed to providing dual mode cathodes of the type disclosed herein. In that regard, the prior art has not employed the specific combinations and ranges of materials utilized in the practice of the present invention, and cannot achieve the beneficial results obtained through the use of the present invention.